Previous work from our laboratory has led to the conclusion that the inorganic anions, chloride, sulfate and phosphate, utilize different permeability pathways to cross the plasma membrane of the Ehrlich-Lettre ascites tumor cell. This conclusion is based, in part, on the effect of two substituted stilbenes (SITS; 4-acetamido, 4'-isothiocyano-stilbene,2,2' disulfonate and DIDS; 4,4'-isothiocyano-stilbene, 2,2' disulfonate) on the steady state transport of in inorganic anions. For example, irreversibly or covalently bound SITS or DIDS completely inhibits sulfate transport but is without effect on the transmembrane movement of chloride or phosphate. This observation suggests that these agents interact directly with the membrane component responsible for mediating sulfate transport. Consequently, during the coming year we plan to obtain both radio-labeled DIDS and SITS. Tumor cells will be reacted with these agents and the relationship between stilbene binding and inhibition of sulfate transport determined. After the total number of binding sites has been established, cells will be fractionated and the plasma membrane isolated. The association of the labeled stilbene with membrane protein will be determined using gel electrophoresis. BIBLIOGRAPHIC REFERENCES: Levinson, C. and M.L. Villereal. The transport of chloride in Ehrlich ascites tumor cells. J. Cell. Physiol. 88: 181-192, 1976. Levinson, C. The interaction of chloride with the sulfate transport system of Ehrlich ascites tumor cells. J. Cell. Physiol. 87:235-244, 1976.